Reprocessing of spent nuclear fuel, e.g. PUREX™ reprocessing, generates nuclear off-gas that contains several radioactive isotopes, including gaseous 129I and noble gases 85Kr and 133Xe. Entrapping noble gas nuclides for permanent disposal is technically challenging because they are chemically inert. Only very aggressive agents, such as fluorine, can form compounds with noble gas nuclides. The half-lives of 85Kr and 133Xe are 10.7 years and 5.3 days, respectively. As the half-life of 133Xe is sufficiently short, the Xe activity would be negligible if the spent fuel were stored for several months before reprocessing. Therefore, the separation and capture of 85Kr becomes a key issue in trapping radioactive noble gases.
Several methods have been proposed for trapping radioactive noble gas streams from the off-gas. These methods include cryogenic distillation and membrane separation. The cryogenic distillation process is well understood. However, the drawbacks include higher operating cost and the potential for fire hazard because of ozone accumulation. The membrane separation process also has high operating cost and low throughput, or efficiency.
Activated carbon is one known adsorbent, which has a high capacity to adsorb noble gases. In addition, activated carbon is relatively inexpensive in comparison to the cryogenic and membrane separation methods. Activated carbon, however, poses a significant fire hazard. For trapping of noble gases, and particularly trapping of radioactive 85Kr, an activated carbon adsorbent that does not pose a significant fire hazard would provide economical and efficient permanent disposal or long-term storage options. Such an activated carbon would therefore be desirable.
In addition, activated carbon adsorbents that do not pose a significant fire risk would be desirable in other industries. For instance, in the chemical and petrochemical industries, activated carbon adsorbers are used to control emissions of solvents and other volatile organic compounds (VOC's) from process streams, off-gases and tank ventings. The volatile organic compounds associated with petrochemical industries include, for example and not limited to, benzene, toluene, xylene (o-, p-, m-isomers), petroleum distillate fractions (naphtha), 2-butoxyethanol, and ethyl benzene.
In the fields of environmental engineering, nuclear, military, and specialist extraction, activated carbon is also used to remove VOC's and other chemicals. For example, aliphatic, aromatic, unsaturates and alicyclics hydrocarbons and other pollutants are present in the atmosphere of submarines and are removed by activated carbon beds. Despite their use in these industries, the fire risk posed by the activated carbon is of great concern and there have been a number of fire accidents related to activated carbon ignition. Thus, an advanced, fire-resistant activated carbon material would be desirable in such other industries as well.